This invention relates to a gripper device having flat jaws and being particularly useful for transporting and registering plates, flexible sheets, and the like substrates on single or multicolor silk screen printers.
As a rule, the plates or sheets of cloth, paper, or the like, to be overprinted on silk screen printers are fed into the printing stations from a pack of such plates or sheets. To this aim, each individual sheet is picked up and transported flat by grippers which can be shifted in timed relationship with the printing operations.
To ensure that the individual sheets, or plates, can be picked up always on the same plane, i.e. the plane containing the sheet itself, it is common practice to use twin jaw grippers wherein one jaw is held stationary and the other spread open or otherwise lifted from the stationary one, thus permitting a gripper to be opened and closed, and the sheet or plate to be correspondingly released and gripped.
These prior grippers have some practical disadvantages, especially where the sheets or plates to be transported comprise a material lacking adequate rigidity of its own. In this case, in fact, it may happen that a margin edge of a sheet being picked up does not lay true, for reasons due to deformation of the sheet itself, against the support surface and fails to enter, or only enters irregularly, the nip between the gripper jaws.